The invention relates to a resonant converter.
In converters of this type a d-c voltage carried on the input side is first chopped and the a-c voltage thus produced in the form of a chopped d-c voltage is processed by means of circuit parts containing resonant circuit elements.
Transformers, particularly ones that produce an electrical separation of the input and output side of the converter, are used for this purpose. With converters of this type it is possible to manufacture inexpensive, small, lightweight power supply units/switched-mode power supplies, which can advantageously be used in consumer electronics appliances such as set top boxes, satellite receivers, television sets, computer monitors, video recorders and compact audio systems. In these applications there is often a need for converters that generate multiple output voltages on multiple converter outputs from one input d-c voltage.
The object of the invention is to design a resonant converter having multiple outputs, two of which are adjustable separately from one another, that is as cost-effective as possible.
The object is achieved in that the converter has multiple outputs and contains a transformer having a primary winding and at least two secondary windings with different winding directions.
With this approach it is possible to provide a converter, which has only one diode (power semiconductor element) in each branched output coupled to a secondary winding; the number of diodes needed in the branched outputs is therefore reduced to a minimum. Two output voltages or output currents generated from one input voltage can be adjusted separately from one another and therefore adjusted to preset values with improved tolerances compared to conventional resonant converters; the converter according to the invention is moreover capable of generating multiple preset output voltages and one or more preset output currents simultaneously. Furthermore, a more cost-effective transformer can be used over a wide output voltage range, since the groups of secondary windings with different winding directions may have different ratios of output voltage generated to number of turns in the associated secondary winding.
If the transformer has a first group of secondary windings with one or more secondary windings having a first winding direction and a second group of secondary windings with one or more secondary windings having a second winding direction, secondary windings can be electrically separated from one another or electrically coupled to one another, the secondary windings in the latter case being coupled, in particular, to a ground potential. The secondary windings may be connected in series, tappings then being provided between the secondary windings.
The resonance frequency of the resonant converter is determined by inductive and capacitive elements of the resonant converter, which take the form of one or more capacitors and/or coils and the transformer main inductance together with the transformer leakage inductances. The resonant frequency of the converter can be adjusted to the desired value, in particular, through additional separate coils, even where this value cannot be set solely by means of a specific transformer design having a preset main inductance and preset leakage inductances.
In one embodiment of the resonant converter, switching elements are used to chop an input d-c voltage and a feedback loop with a regulating circuit serves for regulating two output voltages. Here the frequency and the duty cycle of the chopped input d-c voltage are provided as regulating control variables, it being sufficient to provide a measuring signal for the regulating circuit from just one of the associated output voltages for just one group of identically-wound secondary windings at a time. In the case of the converter according to the invention it is sufficient to couple each of the secondary windings of the transformer to the converter outputs by way of one diode and one output filter each. In particular, different ratios of output voltage to number of turns can be provided in respect of associated secondary windings having different winding directions, so that the distribution of the overall output power generated by the converter can be influenced by presetting these ratios accordingly. At the same time a further converter output voltage range is feasible using simple transformer designs.